1. The correct response is: Ça va, et toi?
This literally translates to "It's going, and you," but really means "I'm good, what about you?" It may sound strange, but the answer to "Ça va?" is the same: Ça va. You can add more words to it, for example "Ça va bien" if you're doing really well, or "Ça va mal" if you're not doing so great.
2. A potential response could be: Pendant les vacances, je suis allé(e) à la plage avec ma famille, et j'ai voyagé à un autre pays.
This says: During vacation, I went to the beach with my family, and I traveled to another country. "Je suis allé(e)" is in the passé composé form (add an "e" at the end of "allé" if you are a woman), as well as "J'ai voyagé."
3. A potential question could be: Et toi, qu'est-ce que tu as fait pendant les vacances?
This says: And you, what did you do during vacation? We can infer that this is the correct question due to Fabien's response (I stayed in Paris with my family. We rode bikes a lot and visited some museums).
